The following aspect interpretations apply only to natal or birth charts. Please see Synastry aspects for comparison charts, and Interpreting transits for transit aspects.
Those with the Moon in opposition to Neptune in their chart find themselves in emotional quandaries quite often. This is due to the constant push-and-pull between the comfort-desiring Moon and wish-upon-a-star Neptune. Their Moon wants to keep rooted, centered, to stop any negative influences on the native, but the Neptune strives to keep them inspired, to see them reach for the stars. Clearly, the Moon, preoccupied with keeping the natives' feet fully on the "ground" (even if this ground is something like the flights of fancy of Pisces or the nervous curiosity of Gemini), is upset by the "shenanigans" of Neptune. Neptune, meanwhile, is constantly stymied by the Moon's constantly calm nature. This leads to instability within the native; whenever they pursue their dreams, they feel reckless and unstable, yet when they go back to that stability they still feel a yearning to fulfill their innermost dreams.